The invention relates to a device for producing drilled holes with an undercut in facing panels. A drilling machine for making a drilled hole with an undercut is known including at least one drill bit at the shank end of which there is provided a drill head for producing the undercut, and a table on which a facing panel is secured.
The prior art discloses devices for producing drilled holes with an undercut and which have a bearing bush with a concave depression in which a drill bit provided with a collar is supported and pivotally mounted. By pivoting-out the drill bit while simultaneously moving it with a circular motion, the lateral cutting edges formed on the drill bit ream out an undercut in the region of the bottom of the drilled hole, into which an expansible fixing plug with an expansible sleeve can be inserted with a matching fit.
Such drilled holes with an undercut can also be made in facing panels or similar structures, but in that case the undercuts have to be made very precisely, so that when inserting and expanding an expansible anchor, the generated expansion pressure is not too great. Too great an expansion pressure can result in a part of the facing panel breaking away. To produce a precise undercut, drill bits which have a drill head tipped with diamond chips are used. The truncated cone-shaped drill head can be provided on its outer peripheral surface and on its end face with diamond chips so that both the bore and the undercut can be made with a single drill bit. When using such a drill bit, several bores with undercuts can be made on the rear side of a facing panel. To ream out the undercuts, the drilling devices conventionally have to be swivelled by hand. Since a high accuracy is required for an undercut of this type, this operation requires good concentration and is comparatively time-consuming.